The present invention relates to a flat display device and, more particularly, to a flat display device including a condenser substrate on which condenser means such as microlenses are formed in one-to-one correspondence with pixels of a display panel.
Recently, flat display devices having high density and large capacity and yet capable of obtaining high display quality are beginning to be put into practical use. In these flat display devices, active matrix type liquid crystal displays using thin film transistors (to be referred to as TFTs hereinafter) as elements for driving pixels are often used, since no cross talk exists between adjacent pixel electrodes, high contrast display can be obtained, and a large screen is readily formable because transmission type display is possible.
Driving elements of such liquid crystal displays are a TFT using amorphous silicon (to be referred to as a-Si hereinafter), i.e., an a-SiTFT and a TFT using polysilicon (to be referred to as p-Si hereinafter), i.e., a p-SiTFT. These driving elements are already commercially available.
A p-SiTFT has higher electron mobility than that of an a-SiTFT, can decrease the size of a driving element, and can improve the pixel aperture ratio on a pixel electrode. Additionally, a p-SiTFT allows circuits for driving scanning lines and signal lines to be integrally formed on an active matrix substrate. This obviates the work of externally attaching driving ICs and the like to a liquid crystal display panel. Since this simplifies the packaging process, the cost can be reduced.
Large screen display can be realized by forming a high-resolution active matrix liquid crystal display by using such p-TFTs and projecting images in enlarged scale by using a projecting lens. Therefore, a front data projector which projects images from the front side of a screen and a rear projection TV which projects images from the back side of a screen are developed.
In such projection type liquid crystal displays, miniaturization of liquid crystal panels is being desired in order to reduce the dimensions, weight, and cost of projector mechanisms. Meanwhile, to increase the brightness of a screen it is being attempted to increase the aperture ratio of a liquid crystal display and improve the efficiency of an optical system by using a high-luminance, high-power light source.
If the resolution is increased while the dimensions of a liquid crystal panel are kept small, the aperture ratio decreases. Hence, it is being attempted to effectively increase the pixel aperture ratio by condensing incident light to a pixel opening by using a microlens substrate.
Unfortunately, the above liquid crystal display has the following problem. That is, an ion exchange substrate is used as a micro lens substrate, and ion exchange microlenses require a soda glass substrate. A soda glass substrate has a thermal expansion coefficient twice or more that of glass generally used in a liquid crystal panel. Therefore, when light irradiates the panel with illuminance increased as the resolution of a liquid crystal display increases, thermal expansion shifts the positions of a pixel opening in the liquid crystal display and a microlens of a microlens substrate from each other. To eliminate this problem, various substrates in which convex lenses are formed on the surface of a glass substrate are being developed as microlens substrates.
FIG. 9 shows the structure of a flat display device, relevant to the present invention, which uses an ion exchange microlens substrate 51 as described above. An array substrate 11 on which TFTs 12 are formed as switching elements and a counter substrate 15 are opposed to each other and attached by a sealing member 13 with a liquid crystal composition 14 being sandwiched between them, thereby constructing a liquid crystal panel 10. The microlens substrate 51 is mounted on the surface of this liquid crystal panel 10. In this microlens substrate 51, microlenses 52 which are high-refractive-index regions are formed in one surface of a glass substrate. Since the surface of this microlens substrate 51 is flat, the microlens substrate 51 is adhered to the counter substrate 15 of the liquid crystal panel 10 by using an ultraviolet-curing adhesive 53.
In the case of ion exchange microlenses, an adhesive having the same refractive index as that of glass can be used as the ultraviolet-curing adhesive 53, so the degree of freedom of choosing an adhesive is large. However, the ion exchange microlenses have problems such as a large thermal expansion coefficient as described above and hence cannot meet the demands on high resolution in the future. Additionally, such microlenses cannot be peeled because they are adhered to a liquid crystal panel over the entire surface. Accordingly, even if the microlens substrate 51 is damaged after the adhesion, so-called rework is impossible by which the microlens substrate 51 is peeled from the liquid crystal panel 10 to reuse the expensive liquid crystal panel 10.
As microlenses capable of meeting the demands on high resolution of liquid crystal panels, a method is beginning to be employed by which convex lenses are formed by using a resin on a glass substrate or by dry-etching a glass substrate. FIG. 10 shows the structure of this liquid crystal display. A microlens substrate 31 is manufactured by forming convex lenses 32 on the surface of a glass substrate. This microlens substrate 31 is so placed that these convex lenses 32 oppose the surface of a liquid crystal panel 10, and is adhered to the liquid crystal panel 10 with a low-refractive-index adhesive 32 being interposed between them. Alternatively, the liquid crystal panel and the microlens substrate are adhered by an adhesive with an air layer being interposed between them.
When, however, the counter substrate and the microlens substrate are adhered over the entire surfaces by the low-refractive-index adhesive as in the former case, the low-refractive-index adhesive is expensive, and the adhered members readily peel. When these members are adhered via an air layer as in the latter case, reflection occurs in two interfaces owing to the existence of the air layer, and this causes light amount loss each time reflection occurs. Furthermore, moisture easily enters between the substrates to cause clouding.
As described above, liquid crystal displays relevant to the present invention have the problems that light amount loss occurs between a microlens substrate and a display panel and the cost is high.
It is, therefore, an object of the present invention to provide a flat display device capable of suppressing light amount loss between a condenser substrate and a display panel and reducing the cost.
According to the present invention, there is provided a flat display device comprising a flat display panel having a plurality of pixels, and a condenser substrate having a plurality of condenser means formed in one-to-one correspondence with the pixels of the display panel, wherein the display panel and the condenser substrate are attached via a liquid layer.
As described above, the condenser substrate and the liquid crystal panel are attached via the liquid layer having a lower reflective index than that of the condenser means. This suppresses light amount loss caused by interface reflection. Also, the liquid layer prevents mixing of moisture or dust, which occurs when an air layer is interposed, and thereby improves the reliability of the device. When the condenser substrate is adhered to the display panel over the entire surface by using an adhesive, the degree of freedom of selecting an optimum refractive index is low. However, in the present invention, the condenser characteristics can be optimized with relative ease by controlling the refractive index of the liquid layer. Furthermore, when surface adhesion is performed, distortions are produced by volume shrinkage during ultraviolet curing, the adhesive generates birefringence, the microlens characteristics are adversely affected, and local peeling occurs in a peripheral portion when a reliability test is conducted. The present invention can also prevent these inconveniences.
The display panel and the condenser substrate may be attached via a sealing member formed in a peripheral portion of a display region in the display panel and the liquid layer injected inside the sealing member and having a refractive index lower than that of the condenser means.
A gap control member for controlling a gap between the display panel and the condenser substrate may be mixed in the sealing member.
The liquid layer may contain at least one of ethylene glycol and glycerin.
The liquid layer may contain perfluoropolyether.
The liquid layer may contain fluorosilicone oil.
The condenser means may be made of an organic material.
At least one of a protective film and an antireflection film is desirably formed on at least one of a surface of the condenser means of the condenser substrate and a surface of the condenser substrate, which is opposite to a surface facing the display panel.
The condenser substrate may be a microlens substrate or a holographic color filter.
A flat display device of the present invention is a display device comprising a display panel having a plurality of pixels and a condenser substrate having a plurality of condenser means formed in one-to-one correspondence with the pixels of the display panel, wherein a first peripheral region having height different from an apex height of the condenser means is formed outside a region of the condenser substrate in which the condenser means are formed, and a second peripheral region having substantially the same height as the apex height of the condenser means is formed outside the first peripheral region.
As described above, a portion to be adhered to a microlens substrate and a counter substrate of a display panel has substantially the same height as a lens portion. This improves the uniformity of the distance between the microlens substrate and the counter substrate, reduces variations in the transmittance characteristics, and prevents degradation of the display quality such as display irregularity.
Although the second peripheral region and the condenser means are desirably made of the same material, they can also be formed in different steps by using the same material or different materials.
The condenser substrate can be adhered to the liquid crystal panel in a region including the second peripheral region. By fixing the condenser substrate and the liquid crystal panel in the second peripheral region having substantially the same height as the condenser means, the distance between the condenser means and the liquid crystal panel can be made uniform.
An alignment mark used to align the display panel and the condenser substrate may be formed in the first peripheral region.
A liquid layer may be interposed in at least a display region between the display panel and the condenser substrate.
To facilitate injecting the liquid layer into at least the display region between the display panel and the condenser substrate, a portion of the first peripheral region may be extended to an end of the condenser substrate.
A flat display device of the present invention comprises a flat display panel having a plurality of pixels and a condenser substrate having a plurality of condenser means formed in one-to-one correspondence with the pixels of the display panel, wherein the display panel and the condenser substrate are attached by an ultraviolet-curing resin with a liquid layer being interposed between them.
A peripheral portion of the condenser substrate may be sealed with a sealing agent.
The sealing agent can fix the flat display device and a holding member for holding the flat display device.
The liquid layer may contain at least one of ethylene glycol and glycerin.
The liquid layer can contain perfluoropolyether.
The liquid layer may contain fluorosilicone oil.
The condenser means may be made of an organic material.
A protective layer made of an inorganic or organic material is desirably formed on a surface of the condenser means, which is in contact with the liquid layer.
An antireflection film may be formed on a surface of the condenser substrate, which is opposite to a surface facing the display panel.
The condenser substrate may be a microlens substrate or a holographic color filter.